Mobile terminals are widely used to provide a variety of communications, multimedia, and/or data processing capabilities. For instance, mobile terminals, such as cell phones, personal digital assistants, and/or laptop computers, may provide storage and/or access to data in a wide variety of multimedia formats, including text, pictures, music, and/or video.
Instant messaging (IM) and Voice Over Internet Protocol (VoIP) are types of communications services that enable users of mobile and/or stationary terminals to communicate in real time over the Internet. For example, in a typical IM application, such as MSN Messenger™, a user may prepare and transmit a text message for delivery to one or more other users of the IM application, typically on a so-called “buddy list”. The messages may be transmitted to the other users based on the “usernames” chosen by the other users for that IM application. As such, conventional IM applications may require registration with a server that maintains user information including the separate usernames, and may require addressing using the separate usernames by those registered in the same IM network. Thus, it may not be possible to send an MSN™ message to other users if they are not using MSN Messenger™. Similar problems may exist in conventional VoIP applications. For example, in the Skype™ VoIP application, it may not be possible to place a Skype™ call to another user unless he is also using Skype™, which may limit the ability to communicate with others.
As such, in order to communicate with others using these applications, users may be required to inform other users of their new usernames and/or may require the other users to install the same application. Thus, users may be required to remember several different ways of contacting the same person. Also with IM applications, many users may need to be logged on to communicate with each other. As such, an IM service may require some number (i.e., a “critical mass”) of people already using (i.e., registered in and logged on to) the IM server in order to send and/or receive messages. Accordingly, many existing IM and/or VoIP solutions for establishing communications connections between mobile terminals may suffer from several drawbacks.
The IP Multimedia Subsystem (IMS) is a standardized Next Generation Networking (NGN) architecture that may be used to provide multimedia services for users of mobile terminals. IMS may use a VoIP implementation based on a 3rd Generation Partnership Project (3GPP) standardized implementation of Session Initiation Protocol (SIP), and may run over the standard Internet Protocol (IP). Existing phone systems (both packet-switched and circuit-switched) may be supported. A multimedia session between two IMS users, between an IMS user and a user on the Internet, and between two users on the Internet may be established using exactly the same protocol. Moreover, the interfaces for service developers may be based on IP protocols. As such, IMS may merge the Internet with the cellular world by using cellular technologies to provide access and Internet technologies to provide services. However, in order to establish a multimedia session between two IMS users, SIP proxy and/or registrar elements may be required to be implemented in each network that is used to connect the two users. As such, establishing a multimedia session between two mobile terminals using IMS may be somewhat cumbersome.